Circuits drawn with the pen make LEDs light up and give a 3D antenna its juice.

Gel pens, beloved by middle-school girls, are good for decorating cootie catchers, evading laboratory ink analysis, and not much else. But if you replace that metallic ink with real silver, you get something quite remarkable: a pen that can draw functioning circuits on paper.

Engineers at the University of Illinois have built such a device and used it to put together several clever electronic doodads. Silver is a conductor, so it ferries electrons from a power source, like a battery, to an outlet, like an LED light, even when it’s just a line on a piece of paper instead of a wire. Once the silver ink dries, it’s as good as wire or printed circuits at conducting electricity, and it survives all kinds of mangling—researchers had to bed the paper back and forth 6,000 times to get the ink to begin to crack and flake off, in fact—so it could be used in situations where flexibility is key. And, of course, just to make cool stuff.

The artifact in question.

To demonstrate their pen-and-paper approach, the researchers drew a copy of a Chinese landscape painting with the pen and affixed an LED to the peak of a house’s roof. Once the silver lines were connected to a battery at the edge of the page, the LED lit up. And by drawing interconnections between LEDs arranged in a grid on a sheet of paper and hooking them up to a battery, they created several glowing block letters. They even built a 3D antenna by drawing lines on a piece of sticky-backed printer paper that they folded around a glass ball.

For anyone looking for a cheap way to built circuits without a printer or any custom equipment, this seems like quite the find. And if you’re looking to relive the 90s, well, it’s good for that too.